1. Field of the Invention
The present invention relates to laminar plastic films such as laminates of a polyolefin with a polyamide. Such films are particularly suited for protecting soils which have been previously treated with fumigants such as methyl bromide and chloropicrin, preventing escape of the applied fumigants until they have completely saturated the soil being treated.
2. Description of the Prior Art
Soil fumigation is employed extensively in certain growing areas in order to pretreat soil prior to planting in an effort to eradicate or reduce inoculum of soil pathogens. In some instances, soils are fumigated when specific diseases that cause unacceptable loses occur. Generally, soil fumigation is employed to treat soil which is to be planted with so called high risk-high value crops including for example, tobacco, strawberries, tomatoes, ornamental plants, and the like. It has been found that in the absence of such fumigation treatment, buildup of soil-born diseases that attack the root systems of such crops will occur and cause unacceptable crop loses. Agricultural soils are routinely fumigated with volatile chemicals such as methyl bromide or mixtures of methyl bromide with chloropicrin. These gases are injected into the soil to be treated with commercially available equipment. Because it may take up to 48 hours, and in some cases a week or more, following treatment before the gases have effectively saturated the soil being treated, and in view of the fumigants' high toxicity as well as the relatively high cost of such gases, it is desirable that the fumigant treated soil be completely covered with a barrier material such as for example, a thermoplastic sheet, immediately after it has been injected into the soil.
Currently in agricultural fumigation of soils, the barrier film which is most commonly employed is a low density polyethylene sheeting. However, it has been found that the conventional low density polyethylene films currently used as fumigant barriers offer only very limited resistance to the penetration of the fumigant vapors so that approximately 1/2 to 2/3 of the fumigant gas, such as methyl bromide and/or chloropicrin, after being applied to a field, escapes through the low density polyethylene barrier film. In addition to the attendant expense of the lost fumigant, there is increased concern regarding the adverse environmental aspects of soil fumigation and the escape into the atmosphere of such highly toxic gases. More stringent regulations limiting atmospheric emissions of this type may be forthcoming from regulatory agencies in the future. Another obvious disadvantage of escaping fumigants is the potential health hazards which are posed for individuals working in the immediate area, as well as residential areas which may surround farms employing such hazardous and toxic fumigant materials. Attempts to replace low density polyethylene films, because of its poor barrier characteristics, with othr materials such as polyester films, saran films and the like, all of which offer some improved barrier characteristics over monolayer low density polyethylene, have met with little success in view of the economic disadvantages attendant with the employment of such costly film substitutes. Unfortunately, until the advent of the present invention, monolayer low density polyethylene film has been the only effective film available in the quantity, cost, and with the physical strength requisites required for commercial fumigation.